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Friday, March 6, 2015

"Smelly Dancers: Waggle-Dancing Bees Use Pheromones." A presentation by Dr. David Gilley.

Updated: Added new link

Recently, Dr. David Gilley, who is an Associate Professor of Biology at William Paterson University, gave two fascinating talks at my local bee club. The first talk was based on the results of research he's been working on. The second talk, which I'll cover in a separate post, was about swarm prevention using biological cues.

Afterward, I was talking to some other beeks, and we all agreed that we wanted to be Dr. Gilley -- or at least have his job. Seriously, anyone who has watched bees for any length of time ends up with all kinds of questions. How awesome would it be if you spent your working life finding answers?

In any case, I wanted to share some of my notes from that day. Also, I would like to thank Dr. Gilley for his gracious permission to use the graphics from his presentation for this post. I also extend my apologies to him in advance if I have misstated any of the data he presented.

Presentation 1: Smelly Dancers: Waggle-Dancing Bees Use Pheromones
During this presentation, Dr. Gilley basically presented his research on the following question: Do waggle-dancing bees use pheromones to communicate?Unique nature of the honey bee's dancing

Most animal communication refers to something directly in the environment or to a motivational state. For instance, a prairie dog might sound an alarm when seeing a hawk overhead (Direct environement). A wolf might bare its teeth and snarl (motivational state).

Waggle dancing is neither of these. It has nothing to do with a motivational state and it doesn't refer to anything in the direct environment. Instead, the dance refers to something quite far away and is symbolic.

Using various techniques such as direction of the dance and the number of waggles, dancing bees tell the bees on the receiving end of the communication key info such as the distance to, direction to, and quality of the food source.

We know that bees dance, but how exactly is the message conveyed to receiver bees? It's unlikely that the dance is perceived visually since the hive is dark. Dr. Gilley noted that removing the wings of a honey bee could stop communication, which suggests that messages might be conveyed visually or acoustically. However, simply playing sounds of honey bees in a hive does not communicate any messages. Could communication be olfactory? Spoiler alert: The answer it turns out, is yes.

Do waggle dancers produce chemical messages?

The first question Dr. Gilley had to answer was whether waggle dancers actually produce chemical messages. To answer this question, he used SPME fibers to take air samples from four separate areas of his observation hive: 1. Dance floor, 2. Near the dance floor, 3. Far from the dance floor, 4. Dance floor at night (when nobody was dancing).

After analyzing the samples, he discovered that there were 4 distinct peaks in the air sample from the dance floor. The spikes were unique compounds that were related to foraging, but they were not really present in samples taken far from the dance floor or at night.

In this image, you can clearly see the spikes in the samples taken from the dance floor and from areas nearby.Gilley, D. Smelly Dancers: Waggle-Dancing Bees Use Pheromones. Presented at: Meeting of the Connecticut Beekeepers Association; March 2015, Woodbury, CT.

Clearly, unique chemical messages were present on the dance floor, but it was still uncertain whether these these distinct compounds were produced by the dancers or by the flowers they were foraging. Further investigation was required.

To determine if the chemical compounds were being emitted by waggle dancers, Dr. Gilley and his team trained foragers to an unscented sugar water feeder placed 100m away from the hive. Bees who foraged at the feeder were marked. Back at the hive, SPME samples were taken from three kinds of bees. These bees included waggle-dancing foragers (which were marked), non-dancing forages (also marked), and non-foraging bees (which were unmarked). This process was performed for 3 bees in each of these categories from 3 colonies for two days.

Results from dancing bees showed lots of peaks, just like the peaks from the dance floor samples. Because the bees had been trained to sugar water, it was concluded that the chemicals came from the bees themselves and not a floral source.

This image shows the results of the SPME samples collected from the bees.Gilley, D. Smelly Dancers: Waggle-Dancing Bees Use Pheromones. Presented at: Meeting of the Connecticut Beekeepers Association; March 2015, Woodbury, CT.

Do waggle-dance compounds play a role in foraging communication?
After determining that waggle-dancing bees do produce pheromones, the next step was to decide what part these pheromones play in foraging communication. This involved a series of experiments.

Experiment 1: Do compounds affect behavior?
Dr. Gilley posited that adding waggle-dance pheromones to the dance floor would increase the number of bees arriving at the feeding station. First, bees were trained to a feeder. Dr. Gilley couldn't get a synthetic version of one of the four waggle-dance pheromones. However, he had the other three compounds (Z-(9)-Tricosene, Tricosane, and Pentacosane) dissolved in hexane, which he called a TTP solution. For the experimental group, the TTP solution was vaporized and injected onto the dance floor. For the control group, hexane was used on the dance floor. Afterwards, his team recorded the number of bees that arrived at the feeder 10 minutes prior to injection and up to 30 minutes after the injection.

They observed that prior to injection, the number of bees at the feeder was about the same from both groups. After the injection, the number of bees exposed to the TTP solution increased dramatically.

Red bars indicate the number of bees expose to the TTP. Blue represents the control group. After the 10-minute mark (which is when TTP was injected onto the dance floor), the number of bees from those colonies increases dramatically.Gilley, D. Smelly Dancers: Waggle-Dancing Bees Use Pheromones. Presented at: Meeting of the Connecticut Beekeepers Association; March 2015, Woodbury, CT.

Clearly, waggle-dance pheromones increased foraging behavior, but how? The next two experiments were dedicated to testing the following hypotheses:

Hypothesis 1: Dance pheromone enhances the recruitment of naive bees because bees may dance more and/or dance more effectively.

Hypothesis 2: Many experienced foragers will not bother decoding waggle dancers because they already know of good food sources. This hypothesis states that dance pheromones may help waggle-dancers activate (recruit) experienced foragers to their source.

Hypothesis 1: Dance pheromone enhances the recruitment of naive bees.

One of the things that Dr. Gilley mentioned is that he still has no idea (and no way to measure) what the normal level of dance pheromones is on a dance floor. However, he predicted that if he just flooded the danced floor with TTP it would increase the effectiveness of the dancing.

For this experiment, he trained bees to a feeder and then marked about 50 of the foragers at the feeder so that they could all be identified individually. After filling the feeder, they'd video record bees dancing. After 30 minutes, they'd flood the dance floor with TTP and record for another 30 minutes to see if the dancing changed. They also captured any unmarked bees that arrived at the feeder so that they could tell how many bees were being recruited by the dancers. From the videos, they counted up the number of dances being made, the duration of these dances, the rate of waggle runs, and the number of dance followers.

They data they collected was analyzed to answer the following questions:

Does dance pheromone increase dance efficacy? No. Dr. Gilley showed some bar graphs that showed that dance efficacy, based on the number of followers per dance, number of captured recruits per waggle run, and number of captured recruits per dance bout, were fairly close for both solvent control groups and for groups exposed to TTP.

Does dance pheromone increase the intensity of each dance? Slightly yes. Dance intensity was based on the number of dance bouts per dancer, the mean dance duration, and waggle-run frequency. The graphs he showed were again fairly close for both control and experimental groups, but the experimental groups showed slightly more intensity.

Does dance pheromone increase the amount of dancing? Yes. The amount of dancing was measured in the morning, afternoon, and evening. For this, they counted dance bouts, waggle runs, and bees engaged in waggle dancing. I thought this figure, shown below, was very interesting because of the clear differences measured between the control & experimental groups. Also, the time of day seems to have made an enormous difference. Based on this measurement, Dr. Gilley concluded that depending upon the time of day, dance pheromone does indeed have an effect on the recruitment of naive bees.

Dance pheromone does have an impact on the amount of dancing.Gilley, D. Smelly Dancers: Waggle-Dancing Bees Use Pheromones. Presented at: Meeting of the Connecticut Beekeepers Association; March 2015, Woodbury, CT.

Dr. Gilley explained how experienced foragers will follow waggle dances but then go to a different source that they have found on previous expeditions. (Bees have and use private information. How cool is that?!) But how do they compare their personal information with the information from the waggle dance? What causes them to make a different choice? Dr. Gilley mentioned that the answer is unknown, but it may have to do with the quality of the dance or level of excitement demonstrated by the dancing bee. The goal of this experiment was to see if adding TTP to the dance floor could increase the recruitment of these experienced foragers to an empty feeding station.

For this experiment, his team trained bees to a sugar water feeder. Bees at the feeder were marked so that they could be individually identified. These bees became the "experienced foragers." Then the feeder was emptied. Before adding TTP to the dance floor, the frequency and the identity of bees at the feeder was recorded for 30 minutes. Then either TTP or hexane control were injected into the experimental/control hives. Again, the frequency and identity of bees at the feeder was recorded for another 30 minutes. Here's what they found.

Increased % of change in total number of visits. They discovered that after injecting the hives, the percent of change in the number of visits to the empty feeder changed dramatically. Hives receiving the solvent control actually saw a negative percent of change (approximately -50%). Hives receiving TTP saw a 100% increase in the number of visits. However, they still had to determine whether there were simply more bees coming to the feeder or whether individual bees were making more trips to the feeder.

Increased % of change in total number of visitors. In terms of the percent of change in the number of visitors to the empty feeding station, the control group again saw a negative percent of change (approximately -50%) whereas the TTP group saw a 50% increase. So visitors from the TTP group were approximately twice as many as those from the control.

Increased % of change in total number of visits by individual bees. Again, the control group saw a negative change, and the experimental group saw an increase in the number of visits by individually marked bees.

Final Words
Dr. Gilley concluded his presentation saying that there is still a lot more information that he needs to gather on waggle-dance pheromones. For instance:

For these experiments, Dr. Gilley's team simply flooded the dance floor with TTP. They don't know what the natural concentration of these pheromones is, and they need to know that to be able to make real comparisons/further studies.

Dr. Gilley's team was only able to identify 4 compounds in the waggle dance. There may be other active or inactive compounds, and that is something else to investigate.

Another thing that isn't really understood yet is how the waggle-dance compounds are transmitted from one bee to another.

Future Goals

Additionally, his team is interested in exploring how the application of these pheromones might affect the longevity and health of the bees.

Papers by Dr. Gilley
If you're interested in reading papers published by Dr. Gilley on this subject you can access the following:

2 comments:

You always take such good notes at your meetings - more than I ever could (and you have much more interesting speakers than at our groups). I'm always amazed at how bee researchers can follow these bees so closely. I sit and watch my hive trying to track a single bee and always lose it in the crowd. It makes sense that they would have to release some sort of pheromone given the darkness of the inside of the hive. Thanks for sharing this interesting information!

Thanks for the compliment, Don, but in this case, I cheated a bit because Dr. Gilley let me have a copy of his presentation. However, I only cheated a little. I had to edit the info down because I took way more notes than I posted! LOL!

You would love one of the stories Dr. Gilley told. It was about how he got hooked on bees. Basically, he had three colonies that all started to swarm at once, and if they did, he'd lose months of research. So as each swarm emerged, he had to spot and capture the queen as she issued out in that ball of bees. Ha! That's some amazing tracking -- must be why he has his job and we don't. ;)